Miniature forward-looking ultrasound imaging mechanism enabled by local shape memory alloy actuator

ABSTRACT

The present invention relates to a new forward-looking ultrasound device including a local actuator embedded inside an elongate member such as a guide wire or catheter. The present invention includes an ultrasound transducer element configured to engage with the local actuator and rotate about an axis of rotation at least when the ultrasound transducer element and the local actuator are engaged. Also disclosed are methods of using the same.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Patent Cooperation TreatyApplication Number PCT/US2009/044218 filed on May 15, 2009, which claimsthe benefit of U.S. Provisional Application No. 61/054,063 filed on May16, 2008, titled “MINIATURE FORWARD-LOOKING ULTRASOUND IMAGING MECHANISMENABLED BY LOCAL SHAPE MEMORY ALLOY ACTUATOR,” and U.S. ProvisionalApplication No. 61/077,111 filed on Jun. 30, 2008, titled “MINIATUREFORWARD-LOOKING ULTRASOUND IMAGING MECHANISM ENABLED BY LOCAL SHAPEMEMORY ALLOY ACTUATOR,” all of which are hereby expressly incorporatedby reference in their entireties.

BACKGROUND

Embodiments disclosed herein concern a miniature actuator which isuseful in intravascular imaging devices including intravascularultrasound (IVUS), and optical coherence tomography (OCT). The miniatureactuator mechanism and ultrasound or OCT imaging device is preferablyembedded in an elongated body such as an intravascular guide wire orcatheter to provide imaging guidance in various interventionalapplications. Description of the Related Art

Coronary artery disease is very serious and often requires an emergencyoperation to save lives. The main cause of coronary artery disease isthe accumulation of plaque inside a person's vasculature, whicheventually occludes blood vessels. Several solutions are available, forexample, balloon angioplasty, rotational atherectomy, and intravascularstents, to open up the clogged section, which is called stenosis.Traditionally, during the operation, surgeons rely on X-ray fluoroscopicimages that are basically planary images showing the external shape ofthe silhouette of the lumen of blood vessels. Unfortunately, with X-rayfluoroscopic images, there is a great deal of uncertainty about theexact extent and orientation of the atherosclerotic lesions responsiblefor the occlusion, making it difficult to find the exact location of thestenosis. In addition, though it is known that restenosis can occur atthe same place, it is difficult to check the condition inside thevessels after surgery. Intravascular imaging would be valuable duringinterventional procedures to facilitate navigation and forintraoperative feedback. For example, the precise placement andappropriate expansion of stents would benefit from simultaneousintravascular imaging. Existing intravascular imaging devices are toolarge and are not flexible enough to be placed simultaneously with otherdevices.

In order to resolve these issues, an ultrasonic transducer device hasbeen utilized for endovascular intervention to visualize the inside ofthe blood vessels. To date, the current technology is mostly based onone or more stationary ultrasound transducers or rotating a singletransducer in parallel to the blood vessels by means of a rotating shaftwhich extends through the length of the catheter to a motor or otherrotary device located outside the patient. These devices havelimitations in incorporating other interventional devices into acombination device for therapeutic aspects. They require a large spaceinside catheter such that there is not enough room to accommodate otherinterventional devices. Also, due to the nature of the rotating shaft,the distal end of the catheter is very stiff and it is hard to navigatethrough tortuous arteries. The high speed rotating shaft alsocontributes to distorted nonuniform images when imaging a tortuous pathin the vasculature. OCT has also been utilized to visualize theintravascular space based on differential reflectance, but most existingOCT devices rely on a rotating fiber optic which extends along thelength of the device. This approach also has problems, for example, themanipulation, spinning and scanning motion required with respect to adelicate glass or polycarbonate optical fiber; the actuator mechanismlocated outside the patient and tip located inside the patient aresignificantly distant from one another, leading to inefficiencies andcontrol issues arising from the torque created by a long, spinningmember; and remote mechanical manipulation and a long spinning elementdistort the image due to non-uniform rotational distortion.

Additionally, current devices are mainly side-looking devices that arenot able to provide valuable information to be used as guidance duringinvasive procedures. Forward-looking ultrasound imaging is essential inguiding an interventional device for treatment in a timely manner. Forexample, when implanting a heart pacemaker, electrical leads need to beimplanted in precise locations. Currently there is no accurateforward-looking imaging device to direct the leads to the rightlocations. Thus, physicians are required to blindly rely on guidecatheters and spend more time than needed when performing procedures.Also, patients are being over exposed to unnecessary radiation and toxiccontrast agents involved with fluoroscopy. Given the numerousdifficulties with current intravascular imaging devices, there is a needfor an improved forward-looking intravascular imaging device.

SUMMARY

One embodiment of the invention is a forward-looking intravascularultrasound device that includes an ultrasound transducer that rotatesaround an axis of rotation and a local actuator configured to cause theultrasound transducer to rotate. The linear actuator includes a movableelement that moves back and forth from a first position to a secondposition. The movable element is connected to at least one SMA actuatorthat is expands or contracts when activated in order to move the movableelement from the first position to the second position or from thesecond position to the first position. The movable element engages theultrasound transducer and causes it to rotate around the axis ofrotation to create a forward-looking sweeping motion. The ultrasoundtransducer may continue to rotate even after it disengages from themovable element due to the moment of inertia of the transducer or someother amplifying force, for example, a biasing force.

One embodiment of the invention is a forward-looking intravascularultrasound device comprising an elongated body having a longitudinalend, an interior surface, an exterior surface, a proximal end, and adistal end; an ultrasound transducer element disposed at least partiallyin the distal end of the elongated body and configured to rotate betweenat least a primary position and a secondary position about an axis ofrotation that is generally normal to the longitudinal axis; and a localactuator comprising a first element, wherein the first element issecured to and does not move relative to the body; a movable element,wherein the movable element is configured to move longitudinallysubstantially parallel to the longitudinal axis between at least a firstposition and a second position, wherein the movable element isconfigured to engage the ultrasound transducer element at least when themovable element moves from the first position to the second position; afirst SMA actuator coupled to the first element and the movable element,wherein the first SMA actuator is configured to switch between anactivated and deactivated state, wherein the movable element moves fromthe first position to the second position upon activation of the firstSMA actuator; and wherein the ultrasound transducer element rotatesabout the axis of rotation at least when the movable element and theultrasound transducer element are engaged and the movable element movesfrom the first position to the second position. In another embodiment,the device comprises a biasing element coupled to the movable elementand the first element, wherein the biasing element is configured to movethe movable element from the second position to the first position. Inyet another embodiment, the biasing element comprises a spring.

In another embodiment, the device described herein comprises a secondelement, wherein the second element is secured to and does not moverelative to the body; and a biasing element coupled to the secondelement and the movable element, wherein the biasing element isconfigured to move the movable element from the second position to thefirst position. In some embodiments, the first and second elements aredisposed along an axis that is substantially parallel to thelongitudinal axis. In other embodiments, the first and second elementsare disposed along an axis that is substantially normal to thelongitudinal axis. In some embodiments, the biasing element comprises aspring. In other embodiments, the biasing element comprises a second SMAactuator, wherein the second SMA actuator has an activated and adeactivated state and when the second SMA actuator is activated itopposes motion of the movable element from the first position to thesecond position. In some embodiments, the cross-sectional shape of thedistal end of the body is generally curvilinear and has a diameter ofnot more than about 0.200 inches.

Some embodiments of the device comprise an electrical wire connected tothe ultrasound transducer element. In some embodiments, the devicecomprises a member coupled with the interior surface of the elongatedbody at or near the distal end, wherein the ultrasound transducerelement is configured to rotate about the member between at least theprimary position and the secondary position. In some embodiments, theelectrical wire is coiled at least partially around the member. In someembodiments, the cam and ultrasound transducer element are notcontinuously engaged while the movable element moves from the secondposition to the first position.

In some embodiments, the angle of rotation the ultrasound transducerelement rotates about the axis of rotation between the primary positionand the secondary position is between about 5° and about 185°. In someembodiments, the angle of rotation the ultrasound transducer elementrotates about the axis of rotation when the movable element moves fromthe first position to the second position is less than the angle ofrotation the ultrasound transducer element rotates about the axis ofrotation between the primary position and the secondary position. Insome embodiments, the linear actuator is not fixed to the ultrasoundtransducer element. In some embodiments, the ultrasound transducer andcam are not engaged after the movable element reaches the secondposition and the ultrasound transducer continues to rotate about theaxis of rotation towards the secondary position. In some embodiments,the ultrasound transducer element comprises a biasing element configuredto bias the ultrasound transducer towards the secondary position. Insome embodiments, the biasing element comprises a spring. In someembodiments, the biasing element comprises an electrical wire. In someembodiments, the ultrasound transducer element comprises a high densitymaterial and a transducer crystal. In some embodiments, the volume ofthe ultrasound transducer element is at least about 0.1 cubic mm. Insome embodiments, the mass of the ultrasound transducer element is atleast about 1 mg. In some embodiments, the ultrasound transducer elementis configured to transmit ultrasound energy at an angle of between about15° and 165° relative to an axis that is generally normal to thelongitudinal axis and the axis of rotation. In some embodiments, theelongated body comprises a guide wire. In some embodiments, the firstelement comprises an aperture, and the movable element is disposed atleast partly within the aperture. In some embodiments, the movableelement comprises a shaft and in some embodiments, the movable elementcomprises a shaft connected to a cam.

Another embodiment is a method of visualizing the interior of apatient's vascular, the method comprising inserting the distal end ofthe distal end of a device disclosed herein into the vasculature of thepatient; generating an ultrasound signal from the ultrasound transducerelement; activating the first SMA actuator such that the movable elementmoves from the first position to the second position and the cam engagesthe ultrasound transducer element; deactivating the first SMA actuatorsuch that the biasing element moves the movable element from the secondposition to the first position; receiving an ultrasound signal reflectedfrom the interior of the vasculature on the ultrasound transducerelement; and producing an image from the reflected signal.

Also disclosed herein is a forward-looking intravascular ultrasounddevice comprising an elongated body having a longitudinal axis, anexterior surface, a proximal end, and a distal end; an ultrasoundtransducer means disposed in the distal end of the elongated body andconfigured to rotate about an axis of rotation that is generally normalto the longitudinal axis; and a local actuator means configured toengage the ultrasound transducer means and cause the ultrasoundtransducer means to rotate about the axis of rotation at least when thelocal actuator means and ultrasound transducer means are engaged.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. IA is a partial cut-away perspective view showing an embodiment ofa forward-looking ultrasound imaging device.

FIG. IB is a partial cut-away side view of the forward-lookingultrasound imaging device depicted in FIG. IA.

FIG. 2 A is a partial cut-away perspective view showing an embodiment ofa local actuator including a movable element.

FIG. 2B is a partial cut-away perspective view showing the localactuator depicted in FIG. 2A with the movable element in a differentposition than shown in FIG. 2A.

FIG. 2C is a partial cut-away side view showing an embodiment of a localactuator.

FIG. 2D is a partial cut-away side view showing an embodiment of a localactuator.

FIG. 2E is a partial cut-away side view showing an embodiment of a localactuator.

FIG. 3A is a diagram showing how the rotational motion of a SMA actuatoris controlled.

FIG. 3B is a diagram showing how the longitudinal motion of a SMAactuator is controlled.

FIG. 4A is a perspective view of an embodiment of an ultrasoundtransducer element configured to rotate about a coupling member.

FIG. 4B is a side view of an embodiment of an ultrasound transducerelement.

FIG. 4C is a side view of an embodiment of an ultrasound transducerelement.

FIG. 5 is a partial cut-away side view of an embodiment of aforward-looking ultrasound imaging device.

FIG. 6A is a partial cut-away side view of an embodiment of aforward-looking ultrasound imaging device.

FIG. 6B is a partial cut-away side view of the forward-lookingultrasound imaging device shown in FIG. 6A showing the ultrasoundtransducer element in a different position.

FIG. 6C is a partial cut-away side view of the forward-lookingultrasound imaging device shown in FIG. 6B showing the ultrasoundtransducer element in a different position.

FIG. 7A is a partial cut-away side view of an embodiment of aforward-looking ultrasound imaging device.

FIG. 7B is a partial cut-away side view of the forward-lookingultrasound imaging device shown in FIG. 7A showing the ultrasoundtransducer element in a different position.

FIG. 7C is a partial cut-away side view of the forward-lookingultrasound imaging device shown in FIG. 7B showing the ultrasoundtransducer element in a different position.

FIG. 7D is a partial cut-away side view χ>f the forward-lookingultrasound imaging device shown in FIG. 7C showing the ultrasoundtransducer element in a different position.

FIG. 8A is a partial cut-away side view of an embodiment of aforward-looking ultrasound imaging device.

FIG. 8B is a partial cut-away side view of the forward-lookingultrasound imaging device shown in FIG. 8A showing the ultrasoundtransducer element in a different position.

FIG. 9A is a diagram showing waveforms of voltage versus time that isused to produce different scanning motions for a transducer element in aforward-looking imaging device.

FIG. 9B is a diagram showing the angle of rotation versus time for atransducer element in a forward-looking imaging device during an activepath and returning path.

FIG. 1 OA is a perspective view of an embodiment of a forward-lookingultrasound imaging device.

FIG. 1OB is a partial cut-away perspective view of an embodiment of aforward-looking ultrasound imaging device.

FIG. 1OC is a partial cut-away side view of an embodiment of aforward-looking ultrasound imaging device.

DETAILED DESCRIPTION

Embodiments disclosed herein relate to imaging devices for intravascularimaging, although the present invention is not limited to this preferredapplication. Imaging of the intravascular space, particularly theinterior walls of the vasculature can be accomplished by a number ofdifferent means. Two of the most common are the use of ultrasoundenergy, commonly known as intravascular ultrasound (IVUS) and opticalcoherence tomography (OCT). Both of these methods are optimized when theinstruments (IVUS or OCT) used for imaging a particular portion of thevasculature are repeatedly swept over the area being image, for example,with a back and forth sweeping motion or rotational sweeping motion.

To address the limitations in current devices, a new intravascularimaging device is described based on a Shape Memory Alloy (SMA) actuatordevice embedded inside an elongated body such as a guide wire orcatheter. Embodiments of the present invention utilizes a novel SMAdevice to provide forward-looking imaging by providing movement for anultrasound transducer or OCT element. Since this novel SMA actuatordevice can be easily fabricated in micro-scale using laser machining orother fabrication techniques, it provides an advantage over existingimaging devices because it offers the ability to miniaturize the overallsize of the device, while the use of multiple transducer crystalsmaximizes field of view. The small dimensions of the actuator device ofthe invention allow for the cross-sectional area of the elongated bodyin which it is housed to be very small. The outside width of theelongated body, such as a guide wire or catheter containing an imagingdevice described herein can be as small as from about 0.0050″ to about0.200″. The outside width for elongated bodies can be larger when theimaging device is combined with other interventional devices, althoughthe outside width of these devices can be as small as 0.060″ or smaller.Current catheters containing IVUS range from 0.70 mm to 3 mm in outsidediameter.

Additionally, embodiments of the present invention address limitationsstemming from fatigue failure due to the range of displacement in SMAactuator devices. Ultrasound devices must be able to operate for acertain period of time when used in invasive procedures. However, thelife of the SMA actuator may be limited by fatigue failure after acertain amount of cycles of scanning. Fatigue failure can be delayed ifthe range of displacement the SMA actuator undergoes is limited. On theother hand, a large scanning motion is required to produce qualityimages during an invasive procedure. Embodiments disclosed hereinbalance these two concerns and incorporate an SMA actuator thatundergoes a small displacement and applies an impulse force on thetransducer. The transducer continues to rotate after the SMA actuatorapplies the impulse force due to the moment of inertia of the transducerand/or another biasing force, for example, a spring. Thus, embodimentsdisclosed herein can produce a large scanning motion while limiting thedisplacement of the SMA actuator and preventing or delaying fatiguefailure of the SMA actuator

Existing single-element ultrasound (IVUS) devices are based on arotating shaft with a driving motor located externally. An imaging tipwith a transducer or mirror is mounted directly on the rotating shaft.As a result, when the rotating shaft has a slight change in its motion,it induces a non-uniform rotational distortion (NURD) in the actualimage. NURD may happen when there is a kink along the length of therotating shaft. Since shafts in current IVUS devices are relatively big,they tend to kink when going through a tortuous path, for example, avasculature, resulting in a NURD problem in imaging. NURD happens insome instances because there is no way of knowing where the imaging tipis pointing if the device is not forward-looking. NURD can be reduced oreliminated if there is a feedback signal available from the distal endas provided in some embodiments disclosed herein.

Embodiments disclosed in this application do not require a rotatingshaft or fiber optic along the length of the catheter, allowing for amore flexible catheter or guide wire, and providing room for otherinterventional devices. In addition, the lack of a rotating shafteliminates the problems mentioned above with current OCT technology, forexample, NURD. Another advantage of some of the embodiments disclosedherein is the elimination of non-uniform distortion of the acquiredimage that occurs in current IVUS devices. In one embodiment, theimaging mechanism (e.g., ultrasound transducer element) is located atthe distal end of the device and does not continuously rotate butoscillates back and forth in a rotational sweeping motion. Additionally,an optional miniature spring can be embedded in the imaging mechanismand work as a position sensor or strain gauge to provide a feedbacksignal to the imaging system.

As used herein, “elongated body” includes any thin, long, flexiblestructure which can be inserted into the vasculature of a patient.Elongated bodies include, for example, intravascular catheters and guidewires. The local actuator is disposed in the distal end of the elongatedbody. As used herein, “distal end” of the elongated body includes theportion of the elongated body that is first inserted into the patientand is typically the most distant from the point of insertion after theelongated body enters the patient. As elongated bodies can be solid,some will include a housing portion at the distal end for receiving thelocal actuator. Such housing portions can be tubular structures attachedto the side of the distal end or attached to the distal end of theelongated body. Other elongated bodies are tubular and have one or morelumens in which the actuator mechanism can be housed at the distal end.

“Connected” and variations thereof as used herein include directconnections, such as being glued or otherwise fastened directly to, on,within, etc. another element, as well as indirect connections where oneor more elements are disposed between the connected elements.

“Secured” and variations thereof as used includes methods by which anelement is directly secured to another element, such as being glued orotherwise fastened directly to, on, within, etc. another element, aswell as indirect means of securing two elements together where one ormore elements are disposed between the secured elements.

Movements which are “counter” are movements in the opposite direction.For example, if the ultrasound transducer element is rotated clockwise,rotation in a counterclockwise direction is a movement which is counterto the clockwise rotation. Similarly, if the movable element is movedsubstantially parallel to the longitudinal axis of the elongate memberin a distal direction, movement substantially parallel to thelongitudinal axis in a proximal direction is a counter movement.

As used herein, “light” or “light energy” encompasses electromagneticradiation in the wavelength range including infrared, visible,ultraviolet, and X rays. The preferred range of wavelengths for OCT isfrom about 400 nm to about 1400 nm. For intravascular applications, thepreferred wavelength is about 1200 to about 1400 nm. Optical fibersinclude fibers of any material which can be used to transmit lightenergy from one end of the fiber to the other.

Embodiments of the invention will now be described with reference to theaccompanying Figures, wherein like numerals refer to like elementsthroughout. The terminology used in the description presented herein isnot intended to be interpreted in any limited or restrictive manner,simply because it is being utilized in conjunction with a detaileddescription of certain specific embodiments of the invention.Furthermore, embodiments of the invention can include several novelfeatures, no single one of which is solely responsible for its desirableattributes or which is essential to practicing the inventions hereindescribed.

FIGS. IA and IB illustrate an embodiment of a novel forward-lookingintravascular ultrasound device 100 capable of sweeping or scanningforward of the distal end of the device 100 to produce IVUS or OCTimages. As shown in FIG. IA, the device 100 may include an elongatedbody 101 having a distal end, a proximal end, and a longitudinal axis.The elongated body 101 is any size. In one embodiment, the elongatedbody 101 is small enough to fit inside a standard guide catheter with aninner diameter that is, is about, is not less than, is not less thanabout, is not more than, or is not more than about 12Fr, HFr, 10Fr, 9Fr,8Fr, 7Fr, 6Fr, 5Fr, 4Fr, 3Fr, 2Fr, IFr, or falls within a range definedby, and including, any two of these values. Thus, the outside diameterof the elongated body 101 is preferably less than the inner diameter ofthe standard guide catheter in some embodiments.

The elongated body 101 has at least a portion 107 which is at leastpartially sonolucent (e.g., permits the passage of at least someultrasound waves without absorbing or reflecting them back to theirsource). The portion 107 can be a window made of an ultrasoundtransparent material, a material which is partially or substantiallytransparent to ultrasound energy, or the portion 107 can be a window,opening, or aperture. In some embodiments, the entire elongated body 101or the majority of the distal end of the elongated body 101 is formed ofa substantially sonolucent material.

In some embodiments, portions of the elongate member 101 are solid andother portions, for example, the distal end, include housing portionscapable of receiving other objects. Such housing portions can be tubularstructures attached to the side of the distal end or attached to thedistal end of the elongated body 101. Other elongated bodies 101 aretubular and have one or more lumens capable of housing other objects inthe distal end. The elongated body 101 shown in FIGS. IA and IB housesan ultrasound transducer element 105, a local actuator 103, a couplingmember 111, and an electrical wire 109. In some embodiments, theelectrical wire 109 is connected to the ultrasound transducer element105 and wrapped at least partially around the coupling member 111. Insome embodiments, the transducer element 105 comprises, or is secureddirectly or indirectly to the coupling member 111.

The local actuator 103 is configured to engage (e.g., contact, push, orpull) the ultrasound transducer element 105 and cause the ultrasoundtransducer element 105 to rotate in a first direction and/or a seconddirection counter to the first direction about an axis of rotation. Insome embodiments, the axis of rotation is generally normal to thelongitudinal axis. In some embodiments, the ultrasound transducerelement 105 is directly connected or coupled with the elongated body 101and configured to rotate relative to the elongated body 101 about anaxis of rotation. In some embodiments, the axis of rotation issubstantially parallel to the coupling member 111. In other embodiments,the ultrasound transducer element 105 is coupled with a member 111 thatextends from an interior surface of the elongated member 101 such thatthe ultrasound transducer element 105 rotates about the member 111.

FIGS. 2 A and 2B show an embodiment of a local actuator 103 thatincludes a first element 205 and a second element 213 which are securedrelative to the interior of the elongated body 101 to anchor or hold thedevice 103 in place relative to the elongated body 101 such that thefirst element 205 and second element 213 do move relative to theelongated body 101. In some embodiments, the first and second elements205, 213 are disposed anywhere within the elongated body 101, forexample, at or near the distal end.

In some embodiments, the local actuator 103 includes a movable element209 that is configured to move relative to the first element 205, thesecond element 213, and the elongated body 101. In some embodiments, themovable element 209, the first element 205, and the second element 213are disposed along an axis within the elongated body 101, for example,an axis that is substantially parallel to the longitudinal axis. In oneembodiment, the movable element 209, the first element 205, and thesecond element 213 are disposed along an axis that is substantiallynormal to the longitudinal axis or an axis that is substantially notparallel to the longitudinal axis. In some embodiments, the movableelement 209 is disposed between the first element 205 and the secondelement 213 and configured to move between the first element 205 and thesecond element 213. In one embodiment, the movable element 209 moves ina first direction along an axis that is substantially parallel to thelongitudinal axis and in a second direction that is counter to the firstdirection. In another embodiment, the movable element 209 is configuredto move in more than one range of motion, for example, along an axisthat is substantially parallel to the longitudinal axis as well asrotationally about the longitudinal axis.

In one embodiment, the first element 205 is connected or coupled withthe movable element 209 by a first shape memory alloy (SMA) actuator 207which moves the movable element 209 when activated as described in moredetail below with reference to FIGS. 3A and 3B. The first SMA actuator207 can be fabricated from any known material with shape memorycharacteristics, for example, nitinol. As known by those of skill in theart, SMAs can be fabricated to take on a predetermined shape whenactivated. In some embodiments, SMAs can be fabricated to expand orcontract when activated from their deactivated state. In otherembodiments, SMAs can be configured to expand or contact and rotate whenactivated from their deactivated state. Activation of a SMA actuatorconsists of heating the SMA such that it adopts its trained shape. Insome embodiments, activation is accomplished by applying an electriccurrent across the SMA element. Deactivation of a SMA actuator can beaccomplished by turning off current to the SMA or otherwise cooling theSMA in order to allow the SMA to return to its pliable state as itcools. In some embodiments, there are electrical contacts and aninsulated area in the local actuator 103 which allow activation of thefirst SMA actuator 207. Activation of the first SMA actuator 207 to itstrained shape results in a force which can be utilized by the localactuator 103 to move the movable element 209 in a first direction, forexample, along an axis between the first element 205 and the secondelement 213.

As one of skill in the art will recognize, SMA actuators can takenumerous shapes and configurations other than the helical shape of thefirst SMA actuator 207 shown in FIG. 1. For example, a SMA is a straightwire, circular wire, or spiral wire. A SMA does not need to have acircular cross-section, for example, it can have a square, rectangular,polygonal, generally curvilinear, or irregularly shaped cross-section.In some embodiments, multiple SMA elements are coupled together to forma single SMA actuator 207. Additionally, other types of actuators, forexample, an electro-magnetic motor, a solenoid, or piezoelectricactuator, can be used in place of a first SMA actuator 207 in the localactuator 103. By alternatively activating and deactivating the first SMAactuator 207, a cyclical movement of the moveable element 209 willresult. This cyclical movement can be rotational about the longitudinalaxis or back and forth along an axis that is generally and/orsubstantially parallel to the longitudinal axis.

The first SMA actuator 207 can be very small such that it has a widthbetween about 5 μm and about 1000 μm, with the preferred size beingbetween about 5 μm and about 100 μm. The first SMA actuator 207preferably has a diameter that is, is about, is at least, is at leastabout, is not more than, is not more than about 5, 10, 20, 30, 40, 50,60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, or 1000 μm,or within a range defined by, and including, any two of these values.The range of lengths preferred for the first SMA actuator 207 in itsrelaxed or deactivated state ranges from about 20 μm to about 10 mm,with the preferred length being from about 200 μm to about 10 mm. Thefirst SMA actuator 207 preferably has an overall length that is, isabout, is at least, is at least about, is not more than, is not morethan about 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600,700, 800, 900 μm, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,17, 18, 19, or 20 mm, or within a range defined by, and including, anytwo of these values.

In some embodiments, the second element 213 is connected or coupled withthe movable element 209 by a biasing element 211. The biasing element211 can be made from materials which are not rigid, including elastic,superelastic, and non-elastic materials. In some embodiments, thebiasing element 211 comprises a spring, for example, a tension spring orcompression spring. In other embodiments, the biasing element 211comprises a second SMA actuator configured to move between activated anddeactivated states. The biasing element 211 can be formed from variousmaterials, including elastic alloys, for example, Cu—Al—Ni, Cu—Al,Cu—Zn—Al, Ti—V, and Ti—Nb alloys.

The biasing element 211 can be very small such that it has a widthbetween about 5 μm and about 1OOOμm, with the preferred size beingbetween about 5 μm and about 1OOμm. The biasing element 211 preferablyhas a diameter or width that is, is about, is at least, is at leastabout, is not more than, is not more than about, 5, 10, 20, 30, 40, 50,60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, or 1000 μm,or within a range defined by, and including, any two of these values.The range of lengths preferred for the biasing element 211 in itsrelaxed or deactivated state ranges from about 20 μm to about 10 mm,with the preferred length being from about 200 μm to about 10 mm. Thebiasing element 211 preferably has an overall length that is, is about,is at least, is at least about, is not more than, is not more thanabout, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600,700, 800, 900 μm, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,17, 18, 19, or 20 mm, or within a range defined by, and including, anytwo of these values.

The biasing element 211 is configured to apply a force to the movableelement 209 that opposes the force applied by the first SMA actuator 207on the movable element 209. This opposing force can move the movableelement 209 in a direction counter to the direction the movable element209 moves when the first SMA actuator is activated. The movement of themovable element 209 can be appreciated by comparing FIGS. 2A and 2B. InFIG. 2A, the movable element 209 is in a first position (e.g., closer tothe second element 213 than the first element 205). In FIG. 2B, themovable element 209 is in a second position (e.g., closer to the firstelement 205 than the second element 213).

In an alternative embodiment, one or both of the first and secondelements 205, 213 are eliminated and one end of the first SMA actuator207 and/or the biasing element 211 are secured directly to the elongatedbody 101 or housing 215. In another alternative embodiment, one or bothof the first and second elements 205, 213 are secured indirectly to theelongated body 101 through an intermediate element, for example, ahousing 215 for the local actuator 103. In some embodiments, the firstSMA actuator 207 is coupled with the movable element 209 and the secondelement 213, and the biasing element 211 is coupled with the movableelement 209 and the first element 213. In another embodiment, the localactuator 103 comprises only a first element 205, a movable element 209,and a single SMA actuator 207 coupled with the movable element 209 andthe first element 205. The single SMA actuator 207 moves the movableelement 209 in a first direction when actuated.

FIGS. 2C-2E show embodiments of a local actuator 103 where a first SMAactuator 207 and biasing element 211 are configured in parallel to oneanother. The first SMA actuator 207 is connected to a first element 205that is secured to and preferably does not move relative to an elongatedbody 101. The other end of the first SMA actuator 207 is coupled with amovable element 209. Similarly, a biasing element 211 is coupled withthe first element 205 and the movable element 209. The biasing element211 can comprise any deformable component, for example, a spring orsecond SMA actuator, and can be configured to apply a force on themovable element 209 that is counter to the force applied on the movableelement by the SMA actuator 207 when the first SMA actuator 207 isactivated. In FIG. 2C, the movable element 209 is disposed between thecam 201 and the first element 205. In FIG. 2D, the first element 205 isdisposed between the movable element 209 and the cam 201. In FIG. 2E,the SMA actuator 207 and the biasing element 211 are disposedconcentrically around the shaft 203. Thus, one of skill in the art willrecognize that a first SMA actuator can optionally be paired withanother biasing element 211 in parallel or series to produce a linearoscillating motion for a connected movable element 209.

As shown in the embodiments in FIGS. 2A-2E, the movable element 209 isconnected to or comprises an arm or shaft 203 such that movement of themovable element 209 results in movement of the shaft 203. The shaft 203can extend from the movable element 209 towards the distal end of theelongated body 101. In some embodiments, the shaft 203 can optionallyextend from the movable element 209 towards the proximal end of theelongated body 101. The first element 205 and second element 213optionally include openings to allow at least a portion of the shaft 203to pass through the first and/or the second elements. One of skill inthe art will recognize that the shaft 203 can be offset such that itdoes not have to pass through the first or second elements 205, 213 inorder to extend through or move past these elements. For example, aportion of the shaft 203 can extend laterally from the movable element209 and then turn and extend along an axis that is generally parallel tothe longitudinal axis. In some embodiments, the shaft 203 itself can beused in place of a movable element 209 by directly connecting the SMAactuator 207 to the shaft 203. In other embodiments, the movable element209 and shaft 203 are an integral component.

A distal end of the shaft 203 is coupled to or comprises a cam 201 thatis configured to move along with the movable element 209 and the shaft203 as the first SMA actuator 207 is alternated between an activated anda deactivated state. The cam 201 is configured to engage, for example,contact, pull, or push, another object. In some embodiments, the cam 201is configured to engage an ultrasound transducer element in order tomove the ultrasound transducer element between at least a primaryposition and a secondary position as the movable element 209 moves backand forth between two positions. In some embodiments, the cam 201 isconfigured to engage an ultrasound transducer element in order to rotatethe ultrasound transducer element between at least a primary positionand a secondary position as the movable element 209 linearly moves backand forth between a first position and a second position. In otherembodiments the shaft 203 directly contacts an ultrasound transducerelement. In some embodiments, the movable element 209, shaft 203, andcam 201 are a single movable piece. In other embodiments, the movableelement 209, shaft 203, and cam 201 are each separate pieces connectedto one another.

In one embodiment, a simple pin joint is disposed between the shaft 203and an ultrasound transducer element. The pin joint, or similarstructure, is configured to convert linear motion into rotationalmotion.

The cam 201, shaft 203, and movable element 209 can be connected invarious configurations. In some embodiments, the shaft 203 comprisesmore than one piece or member that move relative to one another. Forexample, in one embodiment, the shaft 203 comprises a first link that ispivotally connected to the movable element 209 and a second link that ispivotally connected to the first link and the cam 201. In someembodiments, the shaft 203 extends in a direction that is notsubstantially parallel to the longitudinal axis or has a portion thatextends in a direction that is generally normal to the longitudinalaxis. In some embodiments, the shaft 203 may be pivotally connected tothe movable element 209 and/or the cam 201. In some embodiments, theshaft 203 moves relative to the movable element 209 and/or the cam 201.In some embodiments, the cam 201 may move, flex, or deflect, relative tothe shaft 203 and/or movable element 209. In some embodiments, the cam201 is pivotally connected to the shaft 203. In other embodiments, thecam 201 comprises a flexible material.

FIGS. 3 A and 3 B are diagrams showing how the motion of a SMA actuatorcomprised of nitinol is controlled. For the sake of simplicity, FIG. 3Ashows how the rotational motion of a SMA shaft is controlled and FIG. 3Bshows how the longitudinal motion of a SMA shaft is controlled. However,one can combine the configurations illustrated in the two diagrams toachieve both rotational and longitudinal motion simultaneously.

FIG. 3A shows an SMA actuator 207 in a Martensite State and the same SMAactuator 207 in an Austenite State. The SMA actuator 207 is helicallyshaped. In the Martensite State, the SMA actuator 207 has a pitch (e.g.,the height of one full turn) defined as hi, a radius defined as ri, andthe length of the wire making one complete rotation is defined as Li. Inthe Austenite State, the SMA actuator 207 has a pitch defined as h₂ anda radius defined as r₂, and the length of the wire making one completerotation is defined as Li. The relationship between the helix radius,pitch, and wire length is defined by the Pythagorean Theorem as:

(A ₁ f+(2πr _(x) Y=(L ₁)²  [Equation 1] and

(A ₂ Ÿ+(2πr ₂ Y=(L ₂)²  [Equation 2]

Ignoring any contraction effects, the length of the wire wrapped intothe helix remains the same regardless of the helical shape that itforms. To simplify, an assumption can be made that the wire makes onecomplete helical turn in the austenite state. Therefore,

(A ₁ f+(2πr _(x) Y=(L ₁)²  [Equation 3] and

n{h _(x) =h ₂  [Equation 4]

wherein n is the number of turns the helix makes around in theMartensite State. By substituting equations 3 and 4 into equations 1 and2 and solving for n, we are left with the following relationship:

Yn=-  [Equation 5]

This relationship indicates that the maximum achievable rotation isdefined by the ratio of the radii in the Austenite State and theMartensite State. A partial transformation of the nitinol SMA actuator207 from the lower temperature Martensite State to the high temperatureAustenite State will result in a proportional reduction in achievedrotation. One can choose the desired level of rotation by selecting theappropriate ratio between the two radii.

FIG. 3B shows a SMA actuator 207 in a Martensite State and an AusteniteState. In the Martensite State, the SMA actuator 207 has a pitch (e.g.,the height of one full turn) defined as hi and a radius defined as ri,the length of the wire making one complete rotation is defined as Li,and the number of helical turns is defined as nj. In the AusteniteState, the SMA actuator 207 has a pitch defined as h₂ and a radiusdefined as r₂, the length of the wire making one complete rotation isdefined as Li, and the number of helical turns is defined as n₂. Therelationship between the helix radius, pitch, and wire length is definedby the Pythagorean Theorem disclosed in equations 1 and 2. Thelongitudinal motion of the SMA actuator 207 between the Martensite Stateand Austenite State can be determined by the following equation:

Longitudinal motion=(n ₁ Xh ₁)−(n ₂ Xh ₂)  [Equation 6]

FIG. 4A shows an embodiment of an ultrasound transducer element 105 thatincludes a transducer 401, a transducer mount 405, a coupling member111, and an electrical wire 409. The transducer 401 includes at leastone ultrasound transducer crystal configured to send and receiveultrasound signals and the transducer 401 is preferably mounted on abacking 403. The transducer 401 can have various shapes, for example,square or cylindrical. In some embodiments, the transducer 401 isdirectly coupled with a transducer mount 405. The shape and size of thetransducer mount 405 can vary depending on the shape and size of thetransducer 401 or backing 403, to be coupled with the mount 405. In someembodiments, the transducer mount 405 is ring shaped with an aperturethrough the mount 405. In some embodiments, the transducer mount 405includes a recess or indentation configured to receive at least aportion of a cam when the cam is engaged with the transducer mount.

The transducer mount 405 can optionally include a push bar 406configured to engage a cam 201. The push bar 406 can be a pin, bar,cylinder, or similar structure that extends from the body of thetransducer mount 405 to provide a point of contact for a cam 201. Insome embodiments, the cam 201 engages one general side of the push bar406 and in other embodiments, the cam 201 engages more than one side orportion of the push bar 406. In some embodiments, the cam 201 is fixedto the push bar 406 or transducer 405 and in other embodiments, the cam201 is not fixed to the push bar 406.

In some embodiments, the transducer 401 can be made to have a thicknessor length that is between about 5 μm and about 1500 μm, with a preferredsize being between about 5 μm and about 1OOOμm, or more preferablybetween about 200 μm and about 700 μm. The transducer 401 preferably hasa thickness or length that is, is about, is at least, is at least about,is not more than, is not more than about 5, 10, 20, 30, 40, 50, 60, 70,80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200,1300, 1400 or 1500, μm or within a range defined by, and including, anytwo of these values.

In the illustrated embodiment, the transducer mount 405 has or iscoupled with a coupling member 111 such that the transducer mount andtransducer 401 are configured to rotate about the coupling member. Inother embodiments, the transducer mount 405 and/or transducer 401 aredirectly coupled with an elongated body or other fixed object andconfigured to rotate about an axis of rotation relative to the elongatedbody or other fixed object. The coupling member 111 can have variousshapes and sizes depending on the transducer mount 405 and/or thetransducer 401. For example, the coupling member 111 can include acylindrical pin, cylindrical dowel, or differently shaped member. Inother embodiments, the transducer mount 405 and/or transducer 401 areconfigured to rotate about a different revolute joint, for example, acylindrical joint, a screw joint, or a ball and socket joint. Forexample, a transducer mount 405 may include a ball and the elongatedbody 101 may include a socket configured to receive at least a portionof the ball to facilitate rotation of the transducer mount 405 relativeto the elongated body 101. In another example, the transducer mount 405may include one or more pins configured to rotate relative to one ormore openings or sockets in the elongated body 101. Alternatively, thetransducer mount 405 has a socket or opening for a ball or pin disposedon the elongated body 101. In some embodiments, the ultrasoundtransducer element 105 is configured to rotate around an axis ofrotation that is substantially normal to the longitudinal axis. In someembodiments, the ultrasound transducer element 105 is configured torotate around an axis of rotation that is not substantially normal tothe longitudinal axis. In one embodiment, the axis of rotation of theultrasound transducer element 105 may form about a 45 degree angle withthe longitudinal axis.

In some embodiments, the electrical wire 409 is connected to thetransducer 401. For example, in one embodiment, the electrical wire 409is connected to the proximal surface of the transducer 401. In anotherembodiment, multiple electrical wires, for example, two, are connectedto two or more surfaces of the transducer 401. The wire 409 can be thesame as wire 109 in FIG. 1. The wire 409 can connect the transducer 401with an electrical cable, for example, a coaxial or twisted pair, thatis connected to an imaging system. In some embodiments, a wirelesstransmitter (not shown) is used to connect the transducer 401 to animaging system. In some embodiments, the transducer mount 405 acts as anelectrical conductor. In an embodiment, electrical wires 409 are coupledto the transducer 401 through non-contact coupling (e.g., capacitive orinductive coupling) which is commonly used in conventional intravascularimaging systems.

The electrical wire 109 can have various shapes and sizes. For example,the electrical wire 109 can have a generally circular cross-section witha diameter of about 1OOμm. The electrical wire 109 preferably has adiameter that is, is about, is at least, is at least about, is not morethan, is not more than about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40,50, 60, 70, 80, 90, or 100 μm, or within a range defined by, andincluding, any two of these values.

In some embodiments, the electrical wire 409 is wrapped at leastpartially around the coupling member 111 or other portion of thetransducer mount 405 such that it acts to bias the transducer 401 andtransducer mount 405 in a certain direction. In one embodiment, theelectrical wire 409 forms a coil around the coupling member 111 thatacts as a mechanical spring that stores elastic energy as the transducer401 rotates in a first direction and applies the energy to bias thetransducer 401 in a direction counter to the first direction. Thus, theelectrical wire 409 can be used to return the transducer mount 405 andtransducer 401 to a primary position after the transducer mount andtransducer 401 have rotated or moved away from the primary position to asecondary position. Utilizing the electrical wire 409 as a biasing forceeliminates the need for additional force or resistance for the scanningmotion resulting in a device 100 that is more efficient (e.g., requiresless energy) and has a longer scanning time producing better imagingquality. In embodiments where an electrical wire 409 or other structureapplies a biasing force on the transducer mount 405, the device 100requires less energy to operate. One of skill in the art will understandthat a spring or similar biasing structure that is not an electricalwire coiled around the coupling member 111 can also be used to bias thetransducer mount 405 and transducer 401 towards a certain direction orposition.

In a preferred embodiment, the ultrasound transducer element 105 rotatesabout an axis of rotation as another object, for example, a cam, appliesa linear force on the transducer mount 405. In some embodiments, theultrasound transducer element 105 continues to rotate after a force isapplied on the transducer mount due to the moment of inertia of thetransducer 401 and/or transducer mount 405. Generally, the higher momentof inertia is, the more the ultrasound transducer element 105 willcontinue to rotate after a linear force is applied to the transducermount 405. The moment of inertia is mostly determined by the center ofmass of the rotating body and the distance between the center of massand the axis of rotation. Thus, the moment of inertia of the rotatingportions of the ultrasound transducer element 105 can be adjusted byadjusting the mass, size, and location of the rotating portions. Forexample, a longer transducer element 401 is used to increase distancefrom the center of mass of the transducer element 401 and the axis ofrotation.

The size of the ultrasound transducer element 105 itself contributeslargely to the overall ultrasound device 100 size, so it is importantthat a smaller transducer 401 produces an image with quality that iscomparable to a lager transducer 401. Increasing the density of anybacking layer 403 or transducer mount 405 can minimize the transducerlength and overall ultrasound transducer element 105 size.

As shown in FIGS. 4A and 4B, in some embodiments, the moment of inertiaof the rotating portions of the ultrasound transducer element 105 can beincreased by adding a high density material layer 407, optionally thesame as the backing 403. FIG. 4B shows an embodiment of an ultrasoundtransducer element 105 with a high density material layer 407 addedbetween the transducer 401 and the transducer mount 405. The highdensity material layer 407 can comprise any high density material, forexample, stainless steel, tungsten, gold, silver, platinum, copper, ortitanium. FIG. 4C shows another embodiment with a tubular high densitymaterial layer 407 that is placed around the transducer 401 to add massto the rotating elements of the ultrasound transducer element 105. Inother embodiments, a combination of a high density backing layer 407 andtubular structure are used to increase the moment of inertia.

In some embodiments, the volume of the ultrasound transducer element 105is about 0.1 cubic mm. In other embodiments, the volume of theultrasound transducer element 105 is, is about, is at least, is at leastabout, is not more than, is not more than about 0.01, 0.02, 0.03, 0.04,0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16,0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28,0.29, or 0.3 cubic mm. In some embodiments, the mass of the ultrasoundtransducer element 105 is about 1 mg. In other embodiments, the mass ofthe ultrasound transducer element 105 is, is about, is at least, is atleast about, is not more than, is not more than about 0.2, 0.3, 0.4,0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9,1.8, or 2 mg, or within a range defined by, and including, any two ofthese values. In some embodiments, the ultrasound transducer element 105may be generally cylindrical with a diameter or width that is, is about,is at least, is at least about, is not more than, is not more than about0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8,1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3 mm, or withina range defined by, and including, any two of these values. In someembodiments, the ultrasound transducer element 105 has a height that is,is about, is at least, is at least about, is not more than, is not morethan about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2,1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, or 2.5 mm, orwithin a range defined by, and including, any two of these values.

FIG. 5 shows an embodiment of an intravascular ultrasound device 100including a local actuator 103 and an ultrasound transducer element 105configured to rotate about an axis of rotation and a coupling member 111relative to the elongated body 101. The cam 201 of the local actuator103 is configured to move in a first linear direction and a secondlinear direction that is counter to the first linear direction alongwith the movable element 209 (not shown). In some embodiments, whenmoving in a linear direction, the cam 201 engages the transducer mount405 at the push bar 406 and causes the ultrasound transducer element 105to rotate about the axis of rotation in a first direction.

In general, the first SMA actuator 207 is used to generate a largelinear displacement which has intrinsic limitations on how fast it movesand how much power it requires. In some embodiments, because ofgeometric constraints (e.g., the dimensions of a vasculature) the cam201 can collide with the transducer mount 405 other than at the push bar406 when moving in first a linear direction causing the cam 201 to stopmoving in the first linear direction and causing the ultrasoundtransducer element 105 to stop rotating before the desired amount ofrotation of the transducer element 105 is achieved. For example, if thecam 201 is configured to push the transducer mount 405 to cause theultrasound transducer element 105 to rotate, it works fine within acertain angle of rotation (e.g., less than about 60°) but is limitedwhen pushing farther to cause a larger angle of rotation (e.g., up toabout 180°). In some embodiments, when the cam 201 pushes on the pushbar 406 for longer distances, the cam 201 starts colliding with thetransducer mount 405 and the rotation of the ultrasound transducerelement 105 is stopped prematurely.

The problem of the cam 201 colliding with the transducer mount 405 wherenot desired can be addressed by configuring the local actuator 103 toapply an amplified force or impulse force to the ultrasound transducerelement 105. Applying an impulse force to the ultrasound transducerelement 105 utilizes the moment of inertia of the ultrasound transducerelement 105 to rotate the ultrasound transducer element 105 about theaxis of rotation after the cam 201 and the push bar 406 portion of thetransducer mount have disengaged from one another. In one embodiment,the cam 201 pushes the ultrasound transducer element 105 to a certainpoint and the transducer element 105 continues to rotate beyond wherethe cam 201 stops because of the moment of inertia. In embodiments wherethe ultrasound transducer element 105 includes an electrical wire 109,or other elastic element, configured to bias the ultrasound transducerelement 105 in a certain direction counter to the direction of rotationcaused by the impulse force, the ultrasound transducer element 105 willreturn back to a primary position or origin due to the applied biasingforce. In some embodiments, the biasing element 211 in the localactuator 103 is optionally omitted and the electrical wire 409, or otherbiasing element in the transducer element 105, returns the cam 201 andmovable element 209 to the starting position as ultrasound transducerelement 105 rotates to its starting or primary position.

Turning now to FIGS. 6A-6C, an embodiment of an intravascular ultrasounddevice 100 including a local actuator 103 configured to apply an upwardforce on the transducer mount 405 is shown. FIG. 6A shows the cam 201and the transducer mount 405 initially engaged in a primary position.The first SMA actuator 207 is activated to move the movable element 209towards the distal end of the elongated body 101. The shaft 203 and cam201 move along with the movable element 209 and engage the transducermount 405 and push bar 406. The transducer mount 405 begins to rotatecounter-clockwise while the cam 201 continues to move towards the distalend. In another embodiment, if the moment of inertia of the transducerelement 105 is high enough, the shaft 203 can directly push thetransducer mount 405, or the ultrasound transducer element 105, and acam 201 is not necessary to achieve the leverage in the scanning motion.

FIG. 6B shows an example of a point where the movable element 209, shaft203, and cam 201 stop moving towards the distal end and the cam 201 andtransducer mount 405 disengage from one another. At this point, thefirst SMA actuator 207 is preferably deactivated and the biasing element211 causes the movable element 209, shaft 203, and cam 201 to move inthe opposite direction (e.g., towards the position in FIG. 6A). Eventhough the cam 201 and transducer mount 405 disengage at this point, theultrasound transducer element 105 preferably continues to rotatecounter-clockwise about the axis of rotation and coupling member 111.The ultrasound transducer element 105 may continue to rotate about theaxis of rotation after disengagement from the cam 201 because of themoment of inertia of the ultrasound transducer element 105. Thetransducer element 105 may also include an optional biasing element thatassists the continued rotation of the transducer element 105 in thecounter-clockwise direction after the transducer mount 405 disengagesfrom the cam 201. For example, the ultrasound transducer element 105 mayinclude a spring configured to bias the transducer element to rotatecounter-clockwise about the axis of rotation of the coupling member 111.

As shown in FIG. 6C, the ultrasound transducer element 105 can continueto rotate counter-clockwise to a secondary position where the electricalwire 109 or similar structure biases the ultrasound transducer element105 to rotate in a counter direction (e.g., clockwise) back towards itsorigin or primary position. The biasing element 211 will move themovable element 209, shaft 203, and cam 201 back to their initial orprimary position (e.g., the position in FIG. 6A) and the ultrasoundtransducer element 105 can continue rotating until it contacts the cam201 in the first position or until it reaches some other equilibrium.Thus, the oscillating linear movement of the movable element 209, shaft203, and cam 201 can be used to rotate the ultrasound transducer element105 back and forth about an axis of rotation to create a forward-lookingsweeping motion of the transducer 401. In another embodiment, one ormore mechanical stops (not shown) are included to further limit therotation of the ultrasound transducer 105.

The device 100 can be configured for side-looking as well asforward-looking, for example, by placing an ultrasound transducerelement 105 or a reflective surface (not shown) such as a mirror indifferent configurations. In some embodiments, the angle of orientationof the ultrasound transducer element 105 or minor relative to thelongitudinal axis of the device 100 is any angle between about 15° andabout 165°, with the preferred angle for side-looking device 100 beingbetween about 80° and about 110°. Angles contemplated include about 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100,105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, and about165 degrees, or within a range defined by, and including, any two ofthese values.

The range of motion generated by the local actuator 103 described hereinwill vary depending of the application. Rotational motion of thetransducer element can oscillate in a range from about 1 or 2 degrees upto about 270 degrees. The angle of rotational displacement that can begenerated by the local actuator 103 is, is about, is at least, is atleast about, is no more than, or is no more than about, 1, 2, 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100,105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170,175, 180, 190, 200, 210, 220, 230, 240, 250, 260, or 270 degrees, orwithin a range defined by, and including, any two of these values. In apreferred embodiment the transducer 401 scans an equivalent direction toeither side of the longitudinal axis, such that the device 100 isimaging directly in front of the distal tip of the device. Also it ispossible to amplify the angular displacement by simply utilizingdifferent shapes of the transducer mount 405, especially where it has aninteraction/contact with the cam 201. In other embodiments, the scanningmotion is directed to one side of the device, such that the imagingfield is not symmetrical relative to the longitudinal axis. By adjustingthe speed of scanning motion, the scanning rate can be adjusted whilethe device is in the patient, allowing the operator to adjustably definea specific frame rate in real-time images. The preferred range ofrotational displacement or angle of rotation generated by the device 103is from about 30 to 180 degrees. In addition, it is possible to use thedevice 100 for single point interrogation for optical coherencereflectometry or Doppler Effect measurements.

FIGS. 7 A-7D show another embodiment of an intravascular ultrasounddevice 100 where the first SMA actuator 207 is configured to expand andpush the movable element 109 down (e.g., away from the distal end of theelongated body 101) and the biasing element 211 is configured to movethe movable element 209 and cam 201 towards the distal end. When thefirst SMA actuator 207 pushes the movable element 109 down, the shaft203 moves with the movable element and pulls the cam 201 down as well.As the cam 201 moves down, the electrical wire 109 or other biasingforce causes the ultrasound transducer element 105 to rotate clockwise,following the cam. In some embodiments the cam 201 and the transducermount 405 can maintain engagement as the cam 201 moves down. In otherembodiments, the cam 201 and movable element 209 move faster than theultrasound transducer element 105 resulting in disengagement between thecam 201 and the transducer mount 405. The biasing element 211 isconfigured to move the movable element 209 and cam 201 back up to thefirst position shown in FIG. 7A. As the biasing element 211 causes thecam 201 to move towards the distal end to its starting position, the cam201 and transducer mount 405 is engaged, or re-engage, causing theultrasound transducer element 105 to rotate counter-clockwise and returnto its primary or starting position (e.g., the position shown in 7A). Inanother embodiment, the cam 201 is configured to pull the transducermount 405 down, optionally releasing the transducer mount 405 at acertain point. The electrical wire 409 or biasing force then causes theultrasound transducer element 105 to rotate in a counter direction backto its primary position or origin.

FIGS. 8A and 8B show an embodiment where the cam 201 pulls instead ofpushing the push bar 406. FIG. 8A shows the cam 201 and push bar 406initially engaged in a primary position. The first SMA actuator 207 isactivated to move the movable element 209 away from the distal end ofthe elongated body 101 pulling the push bar 406 and causing theultrasound transducer element 105 to rotate clockwise towards asecondary position.

FIG. 8B shows the ultrasound transducer element 105 in the secondaryposition. The ultrasound transducer element 105 can include a biasingelement, for example, a coiled electrical wire 409 or spring (notshown), configured to bias the ultrasound transducer element 105 towardsthe primary position. In some embodiments, the linear actuator 103 doesnot require a biasing element or second SMA actuator 211 to return thecam 201 to the primary position because the biasing element in theultrasound transducer element 105 pulls the cam 201 back to the primaryposition when the first SMA actuator 207 is deactivated. In someembodiments, the local actuator 103 includes a biasing element 211 suchthat the cam 201 pushes and pulls the transducer mount 405 in oppositedirections resulting in a sweeping rotation movement of the ultrasoundtransducer 105.

It is desirable to provide quality imaging for a physician to interpretaccurately during an intervention. There are different ways to improveand achieve higher quality imaging. One way is to have a smooth andconsistent scanning motion. Another way is to acquire as much data aspossible and process the data through averaging and filtering in orderto enhance different characteristics, for example, the signal to noiseratio. Thus, image quality can be enhanced by providing a consistentscanning motion and adjusting the time the scanning motion takes. Toachieve an ideal scanning motion, an actuator drive waveform can beoptimized to produce a consistent motion while maximizing the scanningtime to acquire as much data as possible.

FIG. 9A shows different examples of contemplated waveforms that can leadto different scanning motions. The wave forms are expressed as voltageversus time. FIG. 9B shows how an active heating path and cooling pathaffect rotation of an ultrasound transducer element.

FIG. 9B shows the angle of rotation versus time for an active (heating)path and returning (cooling path).

The ultrasound device 100 must be able to operate for a certain periodof time when used in invasive procedures. Depending on the type ofintervention, the procedure could take a couple of hours or more and theultrasound device 100 could be required to undergo about one million ormore cycles of scanning. In general, SMA actuators are considered tohave low fatigue properties and so it is critical, yet challenging, toachieve the required life cycle with a frame rate of 10 Hz or higher asan imaging device. SMA actuators are able to continuously operate inmillions of cycles so long as they do not undergo a large displacementor strain. The main challenge to achieving a large scanning motionrequired for clinically vital imaging is to balance the displacement ofthe SMA actuator with the fatigue properties of the SMA. For example,typically, a large scanning motion requires a large displacement of anSMA actuator resulting in diminished longevity of the SMA due to fatiguefailure. However, the motion amplification disclosed in a preferredembodiment herein makes it feasible and practical to meet both thedisplacement and fatigue requirements simultaneously. In someembodiments, because of the motion amplification, the SMA actuator 207only needs to produce a small displacement and therefore, undergoes lessstrain while the ultrasound transducer element 105 undergoes a largescanning motion. Thus, embodiments disclosed herein can be used forrelatively long periods of time while still meeting the requirements offunctional imaging devices used in invasive medical procedures.

In some embodiments of an ultrasound device 100, it is desirable toprovide real time imaging without losing valuable information duringintervention. For real time imaging, certain frame rates are preferreddepending on where to image. For example, for heart imaging, it ispreferable to image a moving heart in a frame rate of 20 Hz or higherconsidering how fast it is moving. Conventionally it becomes challengingto drive the first SMA actuator 207 higher than 10 Hz because itrequires enough cooling time to provide a practically functional motion.However, by utilizing the leverage present in preferred embodimentsdisclosed herein, it is possible to achieve a higher frame rate forimaging because the scanning motion is not largely determined by thefirst SMA actuator 207 itself. Also, to be able to drive the first SMAactuator 207 10 Hz or higher, the first SMA actuator 207 is typically incontact with water or other liquid that provides fast cooling. Butembodiments disclosed herein make it possible to drive the first SMAactuator 207 at a frequency that is, is about, is at least, is at leastabout, is not more than, is not more than about 10 Hz, 15 Hz, 20 Hz, 25Hz, 30 Hz or within a range defined by, and including, any two of thesevalues. This makes the manufacturing process for the device simpler andeasier as a commercial product because there is no need to seal or filla device with water or other liquid during assembly and packaging. Bydriving the first SMA actuator 207 in air, it requires less energy anddemands less power from an imaging system.

The first SMA actuator 207 is preferably surrounded by air. Air is agood insulator by itself, so it contributes to a lower operatingtemperature for the device 100 (e.g. the external temperature of thedevice while operating is, is about, is at least, is at least about, isnot more than, is not more than about 25, 30, 35, 40, 43, 45, 50, 55,60, 65, 70 degrees Celsius or within a range defined by, and including,any two of these values) which is more favorable considering possiblenegative effects on tissue when operating at high temperatures. In someembodiments, an optional housing 215 surrounding the first SMA actuator207 (e.g. shown in FIG. 2A) is made of an insulating material thatfurther heat insulates the first SMA actuator 207 from the rest of thedevice 100. Also, air makes the first SMA actuator 207 less susceptibleto the surrounding environment, so it can produce consistent scanningmotion regardless of blood flow, tissue, and body temperature.

The local actuator 103 can generate rotational displacement in a rangefrom about IHz to about 50 Hz. The preferred frequency of motion isbetween about 8 Hz and 30 Hz. The frequency of movement generated by thelocal actuator 103 is, is about, is at least, is at least about, is notmore than, is not more than about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, or 50 Hz, or withina range defined by, and including, any two of these values.

The first SMA actuator 207 can preferably be activated at variousspeeds, depending on the frame rate. Preferably, the first SMA actuator207 is activated at between 0.1 mSec and 50 mSec. It is contemplatedthat the first SMA actuator 207 is preferably activated at a timeconstant that is, is about, is at least, is at least about, is not morethan, is not more than about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8,0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37,38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 mSec, or within arange defined by, and including, any two of these values.

As shown in FIGS. 1OA-1OC, the intravascular ultrasound device 100disclosed herein can be implemented in various medical devices 901, forexample, but not limited to, devices for stent placement and deployment,balloon angioplasty, directional atherectomy, cardiac ablation, PFO(patent foramen ovule) closure, transvascular re-entry, trans-septalpunch, and CTO (chronic total occlusion) crossing. In anotherembodiment, the intravascular ultrasound device 100 can have a lumen oropening along the longitudinal axis configured to introduce a guide wireor other interventional devices, and provide real-time or nearlyreal-time guidance in front of or around the device. Another embodimentof the invention is a method of visualizing the interior of an organ ortissue having a lumen or cavity using the device described above.

For real-time imaging guidance, it is desirable to have a localizedsteering in the distal end of the device 100. In a preferred embodimenta localized steering portion can be incorporated near or around thedistal imaging tip for efficient navigation. The local steering can beactivated by one, two, three, four or more local actuators placed in thedistal end, so it can be remotely controlled. Or the local steering canbe achieved by simple pull wires (one, two, three, four or more)attached to or around the distal end that extends to the proximal end ofthe device, so it can be manually activated by hands. Depending on thenumber of local actuators and pull wires, it can have various motionswith multiple degrees of freedom (one, two, three, four or more).

In some embodiments, the device 100 can provide intravascular ultrasoundimaging in a small device such that it is easier to use in invasiveprocedures. Some medical devices incorporating the device 100 can havean outside diameter that is placed inside a patient's vasculature thatis between about 2Fr and about 3.5Fr (about 0.6 mm to about 1.2 mm),although sizes as small as IFr (0.33 mm) are also contemplated. Forperipheral applications, the outside diameter of the portion of themedical device placed in the patient's vasculature can be as large asabout 12Fr (4 mm). Generally, it is contemplated that the outsidediameter of any portion of the disclosed devices 100, including theproximal and/or distal ends, the main body of the device, or the portionof the device designed to be placed inside the patient, is, is about, isnot less than, is not less than about, is not more than, is not morethan about 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4,1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8,2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2,4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0 mm, or within a range defined by,and including, any two of these values.

In another embodiment, the intravascular ultrasound device 100 iscombined with Fractional Flow Reserve (FFR), so a single device has thecapability of the ultrasound imaging and FFR. FFR is able to measure theintravascular blood pressure which helps in determining the severity ofintravascular stenosis. By combining two methods in a guide wire, asingle guide wire can provide more useful information to guide complexinterventional procedures. In some embodiments, the same transducer 401can be used to do ultrasound imaging as well as pressure measurement. Inother embodiments, a separate sensor can be embedded to measure theintravascular pressure.

The embodiments described above are largely directed to ultrasoundimaging. However, devices incorporating the scanning mechanism are notlimited to cardiovascular applications, and it is contemplated that thedevice can be used in other settings, preferably medical procedures,where visualization of a small lumen or cavity is required.

Although the embodiments described herein have the imaging devices andscanning mechanism located in the distal end of the apparatus or otherelongate member, one of skill in the art will recognize that the imagingdevices can be placed anywhere along the length of the device. Inanother embodiment, the imaging devices disclosed herein are integratedinto the distal end of an device's rigid section that defines the distaltip of an apparatus.

The foregoing description details certain embodiments of the invention.It will be appreciated, however, that no matter how detailed theforegoing appears in text, the invention can be practiced in many ways.As is also stated above, it should be noted that the use of particularterminology when describing certain features or aspects of the inventionshould not be taken to imply that the terminology is being re-definedherein to be restricted to including any specific characteristics of thefeatures or aspects of the invention with which that terminology isassociated. The scope of the invention should therefore be construed inaccordance with the appended claims and any equivalents thereof.

1-32. (canceled)
 33. A forward-looking intravascular ultrasound devicecomprising: an elongated body having a longitudinal axis, an interiorsurface, an exterior surface, a proximal end, and a distal end; anultrasound transducer element disposed at least partially in the distalend of the elongated body and configured to rotate between at least aprimary position and a secondary position about an axis of rotation thatis generally normal to the longitudinal axis; and a local actuatorcomprising a first element, wherein the first element is secured to anddoes not move relative to the body; a movable element, wherein themovable element is configured to move longitudinally substantiallyparallel to the longitudinal axis between at least a first position anda second position, wherein the movable element is configured to engagethe ultrasound transducer element at least when the movable elementmoves from the first position to the second position; and a first SMAactuator coupled to the first element and the movable element, whereinthe first SMA actuator is configured to switch between an activated anddeactivated state, wherein the movable element moves from the firstposition to the second position upon activation of the first SMAactuator; and wherein the ultrasound transducer element rotates aboutthe axis of rotation at least when the movable element and ultrasoundtransducer element are engaged and the movable element moves from thefirst position to the second position.
 34. The device of claim 33,further comprising a biasing element coupled to the movable element andthe first element, wherein the biasing element is configured to move themovable element from the second position to the first position.
 35. Thedevice of claim 33, further comprising: a second element, wherein thesecond element is secured to and does not move relative to the body; anda biasing element coupled to the second element and the movable element,wherein the biasing element is configured to move the movable elementfrom the second position to the first position.
 36. The device of claim35, wherein the first and second elements are disposed along an axisthat is substantially parallel to the longitudinal axis.
 37. The deviceof claim 35, wherein the first and second elements are disposed along anaxis that is substantially normal to the longitudinal axis.
 38. Thedevice of claim 35, wherein the biasing element comprises a second SMAactuator, wherein the second SMA actuator has an activated and adeactivated state and when the second SMA actuator is activated itopposes motion of the movable element from the first position to thesecond position.
 39. The device of claim 38, wherein the movable elementis disposed between the first element and the second element.
 40. Thedevice of claim 33, further comprising an electrical wire connected tothe ultrasound transducer element; the electrical wire configured tobias the ultrasound transducer element towards the primary position. 41.The device of claim 40, further comprising a member coupled with theinterior surface of the elongated body at or near the distal end,wherein the ultrasound transducer element is configured to rotate aboutthe member between at least the primary position and the secondaryposition.
 42. The device of claim 41, wherein the electrical wire iscoiled at least partially around the member.
 43. The device of claim 40,wherein the movable element and ultrasound transducer element are notcontinuously engaged while the movable element moves from the secondposition to the first position.
 44. The device of claim 33, wherein theangle of rotation the ultrasound transducer element rotates about theaxis of rotation between the primary position and the secondary positionis between about 5° and about 185°.
 45. The device of claim 40, whereinthe angle of rotation the ultrasound transducer element rotates aboutthe axis of rotation when the movable element moves from the firstposition to the second position is less than the angle of rotation theultrasound transducer element rotates about the axis of rotation betweenthe primary position and the secondary position.
 46. The device of claim33, wherein the movable element and ultrasound transducer are notengaged after the movable element reaches the second position and theultrasound transducer continues to rotate about the axis of rotationtowards the secondary position.
 47. The device of claim 33, wherein thevolume of the ultrasound transducer element is at least about 0.1 cubicmillimeters.
 48. The device of claim 33, wherein the mass of theultrasound transducer is at least about 1 milligram.
 49. The device ofclaim 33, wherein the first element comprises an aperture, and themovable element is disposed at least partly within the aperture.
 50. Thedevice of claim 33, wherein the movable element comprises a camconnected to a shaft.
 51. A method of visualizing the interior of apatient's vascular, the method comprising: inserting the distal end ofthe apparatus of claim 9 into the vasculature of the patient; generatingan ultrasound signal from the ultrasound transducer element; activatingthe first SMA actuator such that the movable element moves from thefirst position to the second position and the movable element engagesthe ultrasound transducer element; deactivating the first SMA actuatorsuch that the biasing element moves the movable element from the secondposition to the first position; receiving an ultrasonic signal reflectedfrom the interior of the vasculature on the ultrasound transducerelement; and producing an image from the reflected signal.
 52. Aforward-looking intravascular ultrasound device comprising: an elongatedbody having a longitudinal axis, an interior surface, an exteriorsurface, a proximal end, and a distal end; an ultrasound transducermeans disposed in the distal end of the elongated body and configured torotate about an axis of rotation that is generally normal to thelongitudinal axis; and a local actuator means configured to engage theultrasound transducer means and cause the ultrasound transducer means torotate about the axis of rotation at least when the local actuator meansand ultrasound transducer means are engaged.